Process for segregating vapors from liquid



' Oct. 30, 1956 W. H. RUPP PROCESS FOR SEGREGATING VAPORS FROM LIQUID Filed July 31, 1952 m tw@ vm, Qt d u QW H7 W www ma United States Patent O PROCESS FOR SEGREGATINGVAPO FROM LIQUID Walter H. Rupp, Mountainside, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application July 31, 1952, Serial No. 301,950

5l Claims. (Cl. 202-5f3) The present invention is concerned with an improved process for the separation of relatively low boiling constituents from relatively high boiling constituents. The invention is more particularly concerned with a flash operation, wherein a hydrocarbon liquid stream is heated to an elevated temperature and pressure and then passed into a zone wherein the pressure is substantially reduced resulting in vaporization or ilashing of an appreciable portion of the liquid constituents. InV accordance with the present invention the liquid stream before liashing is subdivided into at least two streams which are introduced into a ash zone or tower at different points.

It is well known in the art to carry out various refining operations wherein a liquid stream is heated to an elevated temperature and pressure and introduced into a zone wherein the pressure i-s substantially reduced resulting in rapid flashing or rapid vaporization of at least a part of the liquid constituents. While operations of this character have been entirely successful, certain disadvantages exist. For example, at the point of pressure reduction in the liash zone, relatively high velocities are secured, resulting in entrainment and carryover of liquid particles with the vaporous constituents. This, of course, is undesirable, since the eiciency of separation of the low boiling constituents from the high boiling constituents is materially impaired. In accordance with the present process wherein the liquid stream is subdivided into at least two separate streams which are introduced at separate points of the flash Zone, the velocity of the upflowing -vapors is materially lowered and the carryover of liquid particles ma# terially decreased.

The process of the present invention may be more fully understood by reference to the drawing illustrating one embodiment of the same. For purposes of illustration, the present invention as applied to a vacuum distillation operation is described. Referring specifically to the drawing, a feed oil having a gravity in the range from about 8 A. P. I. to 20 A. P. I. is introduced into a heating zone or furnace 1 by means of feed line 2. In furnace 1 the feed oil is passed through two separate heating coils 20 and 21. The streams are removed from heating coils 20 and 21 by means of lines 3 and 4 and introduced into a low velocity liash zone 5 disposed in the lower area of a flash distillation tower 6. In heating zone 1 the feed streams are heated to a temperature in the range from about 700 F. to 860 F. The pressure on the respective streams is in the range from about l to 20 lbs. p. s. i. g.

The low velocity flash distillation zone comprises two parallel flash sections 7 and 8. The stream withdrawn from heating zone 1 by means of line 3 is introduced into section 7 While the stream removed from furnace 1 by means of line 4 is introduced into section 8. The absolute pressure in each section is substantially equivalent and is in the range from about 30 mm. of mercury absolute to 60 mm. of mercury absolute. The two sections 7 and 8 afford double the vapor area volume as compared to the upper part of tower 6. Hence the vapor velocity in each section is about 1/2 that of tower 6. These low velocity 2,768,940 Patented Oct. 30, 1956 llash zone sections reduce entrainment of heavy, carbonaceous oils into the clean vaporous oils desired as distillate product-s. f

Normally, a ash zone velocity in the range of about 4 to 8 ft. per second at vacuum tower conditions is utilized. This range covers the wide characteristics of the various oils processed. Entrainment of liquid droplets into the vapor stream varies roughly in accordance with Stokes law principles. The lower the entrainment desired, the lower the superficial velocity must be. For example, in a ash tower being described, a ash zone velocity of 2 to 4 ft. per second would be attained by use of two parallel ilash zones 7 and 8. This would reduce entrainment of carbonaceous oils in the upflowing vapor stream by under 50%.

Each flash zone section 7 and 8 includes a wire mesh screen 9 and 11 to assist in coalescing fine oil droplets into larger liquid droplets which then fall downwardly and pass to the bottom of the tower. The liquid stream is withdrawn from the bottom of tower 6 by means of line 17. Vapors rising from section 8 pass through vapor riser 10, and join the vapors rising through zone 7 in the area above screen 9. The velocity in tower 6 above the screen is double that of the' velocity existing in zones 7 and 8. This is permissible since the heavy liquid constituents have been removed from the vaporous stream.

The vapors iiow upwardly in tower 6 and are cooled by means of contacting plates 13 and 14 to the desired temperature. If desirable, a liquid stream may be withdrawn from plate 13 by means of line 15. This stream may be recycled. Overhead vapors are removed from tower 6 by means of line 16, cooled in condenser 22, and passed to a separation zone 23. Uncondensed vapors are removed overhead from separation zone 23 by means of line 24. A liquid condensate is removed as a product stream from separation zone 23 by means of line 25. A portion of this stream may be recycled to the top of tower 6 by means of line 26 as reflux.

The process of the present invention is generally concerned with the utilization of a low velocity flash Zone. The vapors from the respective low velocity flash zones after segregation of the liquid constituents from the vapors are combined to secure a high velocity zone. As pointed out one adaptation of the present invention is applied to a vacuum distillation operation wherein heavy oils are distilled. A typical bottoms from atmospherically-distilled crude oil is one, for example, which has a gravity of about 9 A. P. I.; a ilash point of about 390 F.; a pour point of about and a Conradson carbon content of about 13 or 14%. An oil of this character will have a sulfur content of about 3.6%, and a furol viscosity at 140 F., of about 1400 to 1500 Saybolt seconds.

Another adaptation of the present invention is a vacuum distillation operation where a residuum from an atmospheric pipe still having a gravity of about 5 A. P. I. to 20 A. P. I. is heated to a temperature of about 600 to 900 F. The oil is under a pressure in the range of about l0 to 20 lbs. p. s. i. g., and is passed through a pressure reducing valve or equivalent means into a flash zone, the pressure of which is in the range from about 5 mm. of mercury absolute to about mm. of mercury absolute.

The invention is particularly adapted for operations wherein the oil is heated to a temperature above about 600 F. preferably to a temperature in the range of about 700 F. to 1000 F., and wherein the pressure on the heated stream is sharply reduced -so as to secure vaporization of at least 20% and preferably 40 to 80% of the liquid constituents. This normally means that the pressure on the liquid stream as it passes into the flash zone is abruptly reduced from at least l0 to 20 lbs. or higher per square inch.

What is claimed is:

1. An improved process for segregating relatively low boiling constituents from relatively high boiling constituents which comprises heating a stream comprising liquid constituents of difiere-nt boiling points and vsubjecting said streamtorpressure, segregating said heated stream underpressure into at least two streams, thereafter passing said segregated streams into separate superimposed low velocity ash zones in the lower area of a single flash tower,

maintaining a common vapor combining zone above said ash zones, sharply reducing the pressure on said streams in said flash zones whereby rapid vaporization of the lower boiling constituents occurs, withdrawing condensed liquid from the bottom of said flash tower, maintaining separate paths from each of said ash zones to said vapor combining zone, separately passing vapors from the respective flash Zones into said common vapor combining zone, combining the vapors from said flash zones in said high vapor velocity vapor combining zone of said tower, and witihdrawing vapors from the top of said tower.

2. Process as dened by claim 1 wherein at least 20% of said liquid constituents are vaporized in said flash sections.

3. Process as defined by claim 1 wherein the pressure on said heated liquid streams is abruptly reduced in said flash zones at least 10 lbs. per square inch gauge.

4. Improved process for the vaporization of hydrocarbon constituents from a feed oil having a gravity below about 15 A. P. I. which comprises heating said feed oil at a temperature in the range from about 700 to 860 F. and subjecting said feed oil to a pressure in the range from l0 lbs. to 20 lbs. square inch gauge, segregating said stream into at least two streams, passing said segregated streams into separate superimposed low velocity single flash sections in the lower area of a ash distillation tower, said flash distillation tower being maintained under a pressure in the range from about 30 mm. to 60 mm. of mercury absolute whereby vaporization of the relatively low boiling hydrocarbon constituents occurs in said flash sections, withdrawing liquid constituents from the bottom of said iiash distillation tower, separately combining said vaporized constituents from the respective iiash sections in the upper area of said flash distillation tower, and withdrawing from the top of said hash distillation tower vaporized constituents.

5. Process as defined by claim 4 wherein at least 20% of the liquid constituents are vaporized in said flash sections.

References Cited in the file of this patent UNITED STATES PATENTS 1,145,728 Wiegand July 6, 1915 1,676,895 Gary July 10, 1928 2,274,801 Mills Mar. 3, 1942 .anni 

1. AN IMPROVED PROCESS FOR SEGREGATING RELATIVELY LOW BOILING CONSITUENTS FROM RELATIVELY HIGH BOILING CONSTITUENTS WHICH COMPRISES HEATING A STREAM COMPRISING LIQUID CONSTITUENTS OF DIFFERENT BOILING POINTS AND SUBJECTING SAID STREAM TO PRESSURE, SEGREGATING SAID HEATED STREAM UNDERPRESSURE INTO AT LEAST TWO STREAMS, THEREAFTER PASSING SAID SEGREGATED STREAMS INTO SEPARATE SUPERIMPOSED LOW VELOCITY FLASH ZONES IN THE LOWER AREA OF SINGLE FLASH TOWER, MAINTAINING A COMMON VAPOR COMBINING ZONE ABOVE SAID FLASH ZONES, SHARPLY REDUCING THE PRESSURE ON SAID STREAMS IN SAID FLASH ZONES WHEREBY RAPID VAPORIZATION OF THE LOWER BOILING CONSTITUENTS OCCURS, WITHDRAWING CONDENSED LIQUID FROM THE BOTTOM OF SAID FLASH TOWER, MAINTAINING SEPARATE PATHS FROM EACH OF SAID FLASH ZONES TO SAID VAPOR COMBINING ZONE SEPARATELY PASSING VAPORS FROM THE RESPECTIVE FLASH ZONES INTO SAID COMMON VAPOR COMBINING ZONE, COMBINING THE VAPORS FROM SAID FLASH ZONE IN SAID HIGH VAPOR VELOCITY VAPOR COMBINING ZONE OF SAID TOWER, AND WITHDRAWING VAPORS FROM THE TOP OF SAID TOWER. 